Well I am on the other side of this, I feel so fat even though objectively not overweight at all (BMI of 22, and pretty lean) because I was underweight a long time so in a relative sense I feel fat. I also feel better than I ever did when underweight, physically, and my bone mass is a little better (which is supposed to be impossible to achieve at my age) and that pisses me off, I want my healthiest weight to be the size I like better.

I don’t think it’s good for you to enable them in losing weight, no. Unless you are 100% sure they are not falling into disordered eating. It’s their body, you can’t control that but it’s fine not to support or help them with it.

As someone prone to eating disorders - the suggestion to work out is solid. I find it much better to focus on athletic goals and just let form follow function. It’s good to be able to feel good about what my body can do.